The structure of the Earth

The structure of the Earth

1. The Lithosphere

   • The outer layer of the Earth is called the lithosphere.
     • This layer is relatively cold and rigid and comprises the crust and top part of the mantle.
   • The lithosphere is made of tectonic plates which are less dense than the mantle below.
   • The crust is too thick to drill through, so most of our information about the Earth is collected from seismic waves produced by earthquakes and man-made explosions.

2. The mantle is the zone between the core and the crust. It is cold and rigid just below the crust, but at greater depths it is hot and non-rigid and able to move.

3. The Earth's core transfers energy, so the temperature of the mantle increases with depth.

4. Convection currents slowly move plates.

5. Oceanic crust is denser than continental crust. When these plates collide, the oceanic plate which is cooler at the margins sinks, pulling more of the plate down, and partly melting as it reaches the hotter part of the mantle. This is called subduction.

6. Plate tectonic theory

   • Most scientists now accept the theory of plate tectonics, which suggests that Africa and South America could once have been one land mass, because:
     • - it explains a wide range of evidence
     • - it has been discussed and tested by many scientists.
   • Wegener's continental drift theory 1914 was not accepted by scientists at the time.
   • In the 1960's, new sea floor spreading evidence was found. Subsequent research led to Weigener's theory slowly becoming accepted.

7. Magma and Rocks

   • Magma rises up through the Earth's crust because it is less dense than the crust. This can cause volcanoes.
   • Magma can have different types of composition which cause different types of eruption.
   • Geologists study volcanoes to try to forecast future eruptions and reveal more about the structure of the Earth.
   • Geologists are better able to predict eruptions than they used to be, but still not with 100% certainty.
   • Different types of igneous rock are formed from lava.
   • Iron-rich basalt rock comes from runny lava in slower volcanic eruptions. Silica-rich rhyolite rock comes from thick lava in explosive eruptions.

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